A dual mode moisture and pressure sensor for monitoring critical systems John Dyer MEMS Sensor Analog Front End The Analog front end comprises of 3 sections: • Wheatstone Bridge • Instrumentation Amplifier • Analog To Digital Converter There are two sets of Wheatstone bridges and two sets of instrumentation amplifiers to sense the two pairs of piezo-resistors on the sensor. Instrumentation Amplifier • Each instrumentation amplifier comprises of three operational amplifiers • Discrete operational amplifiers were used to construct this configuration • The ability to set bias voltage is a critical feature • Cannot detect differences below or above the rail voltage Analog To Digital Converter Digital Processing Section The STM32 microcontroller was chosen to handle all the processes after signal is digitized • Communications with the ADC and wireless transceiver Different STM32 MCU’s can perform faster and include more memory while being cross-compatible • Failure detection algorithm It handles the following processes: • Health monitoring algorithms • Temperature monitoring The STM32 can be programmed on its own software with a serial wire debug connection Communications Structures • Several communications layouts are possible and are discussed including: • Hard-Wired Systems • Low Power Transceiver setup • Dedicated board used in handling communications • Minimal power consumption option PCB Prototype Design Enclosure Options